Lines of female mice selected for high and low induced ovulation response are now at generation 14, and selection is being continued with intensive inbreeding. There has been little or no divergence between high and low selected lines. We are looking at the reporductive biology of both males and females of sterile (or semi-sterile) genotypes at the p locus, using transplants of ovary and pituitary and radio-immunoassays of gonadotropins in the sera and pituitary supernatants of affected mice compared to fertile genotypes. We will then attemp to relate our findings to various pleiotropic effects of the p locus, including our initial observation that some fertile genotypes at the p locus gave an enhanced response to injected gonadotropins. Peripheral experiments on the mechanism of vaginal plug formation in rodents are continuing and we also want to determine the primary sex ratio in our pink-eyed stocks of mice, which show a predominance of males at birth and weaning.